Polyurethane foam substrates are widely used materials. Such polymeric substrates are ordinarily manufactured by a casting process in which a mixture of liquid polyurethane-foam-generating reactants are deposited in a mold. Evolution of a gas causes the reactants to foam. For some foam formulations, the reactants themselves react to evolve sufficient gas; in others, a blowing agent is mixed with the reactants to provide gas evolution. Continued gas evolution causes the foam to expand and fill the mold. The foam becomes increasingly viscous as the reactants polymerize, ultimately curing into a polyurethane foam casting shaped by the mold.
Through the years, a number of methods for reducing flammability of flexible cellular products have been reported. One such method involved addition of halogen, antimony or phosphorous containing compounds to the foam reactants prior to fabrication of a product. However, the addition of those compounds impaired physical characteristics of the product. Specifically, flexibility and resiliency were affected. Also, these flame retardant compounds afforded minimal protection against flame penetration because the product melted when contacted by a flame.
A second reported method impregates a preformed cellular material with a flame retardant composition like an ammonium phosphate solution. This method improved resistance to ignition, but the physical characteristics of the impregnated product were inferior.
A third method according to Belgain Pat. No. 841,224, published Oct. 28, 1976, coats flexible polyurethane foam with a flame retardant. The coating can comprise a carboxylated neoprene latex and a mineral hydrate, such as alumina trihydrate. At combustion temperature, the function of the coating is to release water and thereby cool an ignited foam surface. A carbon char is formed during ignition.